1. Field of the Invention
The present invention relates to a motor controlling apparatus which ensures fast starting, stopping or reversing of the motor. More precisely, the invention relates to an automatic focusing device having such a motor controlling apparatus.
2. Description of Related Art
In recent single lens reflex cameras, the number of devices or components incorporated therein, including an automatic focusing device or a powered zoom lens, etc., that are driven by the rotation of the motor, or motors, has increased. The motors repeat frequent starting, stopping and reversing operations. Upon starting, it is necessary for the motors to reach a predetermined rotational speed, or a maximum rotational speed, as quickly as possible. Similarly, upon decelerating, stopping or reversing, the motors must be decelerated, stopped or reversed as quickly as possible. Accordingly, it is necessary to reduce the time required for the accelerating motor to reach a predetermined speed, or to reduce the time required for the decelerating motor to come to a stop.
One of the solutions of this problem would be to provide a mechanical brake as a stopping means. However, this would put limitations on the size and weight of the camera, which is a major consideration in the construction of a compact camera.